New nanosensor sniffs bombs, one molecule at a time

Imagine a piece of metal 30,000 times thinner than one of the
hairs on your head. Mixed with a little protein from bee venom, that
microscopic filament becomes the most powerful explosives-detection system in history, able to detect a single
molecule of dangerous chemicals.

Now imagine having that in an airport. No need for taking a
pornographic photograph or having your genitals massaged by the
Transportation Security Agency. And a nanotechnology
specialist may have hastened that happy day for homeland
security.

Michael Strano, an associate professor of chemical engineering
at the Massachusetts Institute of Technology, spent the past two
years testing out the boundaries of nanotech in explosives
detection. For less than $200,000, he took it practically to the
atomic limit. "There's no further improvement in the sensor part
you can get," Strano tells Wired. "It's the last word in
sensors."

Some of his colleagues aren't quite so sure. Strano's system is
promising, they say. But they have questions about bringing
Strano's sensor into the field.

The science behind the Strano's sensor is complex. But here's
the simplest way of breaking it down. Put bee venom on a carbon rod
and you've got yourself a sensor.

Believe it or not, bees are powerful bomb sleuths. That's
why Darpa wanted to enlist them to find explosives, landmines and
"odors of interest" in the early 2000s. As it turns out, inside of
every bee sting is a small fragment of a protein called a peptide
that has an uncanny property.

"When it wraps around a small wire, that allows it to recognise
'nitro-aromatics'" Strano explains, the chemical class of
explosives like TNT. That wire is a carbon nanotube, a mere one
atom thick.

Put that against a nitro-aromatic treated with the bee peptide,
and take a look through a near-infrared microscope. "The light from
the carbon nanotube will fluoresce -- so red that your eye can't
see it," Strano says. "What you'd see in the microscope is: The
nanotube would flicker off and on." A single molecule of the
explosive material would set off the sensor.

Strano and his team published their work on Tuesday in
the Proceedings of the National Academy of Sciences.

The ion-mobility spectrometers currently used to spot bombs in
US airports are "poor machines" says Ray von Wandruszka, chairman
of the chemistry department at the University of Idaho, who's
worked on atmospheric explosive detection since 1989. The
spectrometers typically detect chemicals in the "low parts per
billion" range. Strano's sensor would be vastly more sensitive.